This invention relates to a method and a device for sawing lumber from workpieces such as cants, and in particular relates to a cant feeding system, for the breakdown of a two-sided cant according to an optimized profile.
It is known that in today""s competitive sawmill environment, it is desirable to quickly process non-straight lumber so as to recover the maximum volume of cut lumber possible from a log or cant. For non-straight lumber, volume optimization means that, with reference to a fixed frame of reference, either the non-straight lumber is moved relative to a gangsaw of circular saws, or the gangsaw is moved relative to the lumber, or a combination of both, so that the saws in the gangsaw may cut an optimized non-straight path along the lumber, so-called curve-sawing.
Advances in digital processing technology and non-contact scanning technology have made possible in the present invention, an orchestrated approach to curve sawing involving a plurality of coordinated machine centers or devices for optimized curve sawing having benefits over the prior art.
A canted log, or xe2x80x9ccantxe2x80x9d, by definition has first and second opposed cut planar faces. In the prior art, cants were fed linearly through a profiler or gang saw so as to produce at least a third planar face either approximately pandallel to the center line of the cant, so called split taper sawing, or approximately parallel to one side of the cant, so called frill taper sawing; or at a slope somewhere between split and flill taper sawing. For straight cants, using these methods for volume recovery of the lumber can be close to optimal. However, logs often have a curvature and usually a curved log will be cut to a shorter length to minimize the loss of recovery due to this curvature. Consequently, in the prior art, various curve sawing techniques have been used to overcome this problem so that longer length lumber with higher recovery may be achieved.
Curve sawing typically uses a mechanical centering system that guides a cant into a secondary break-down machine with chipping heads or saws. This centering action results in the cant following a path very closely parallel to the center line of the cant, thus resulting in split taper chipping or sawing of the cant. Cants that are curve sawn by this technique generally produce longer, wider and stronger boards than is typically possible with a straight sawing technique where the cant has significant curvature.
Curve sawing techniques have also been applied to cut parallel to a curved face of a cant, i.e. full taper sawing. See for example Kenyan, U.S. Pat. No. 4,373,563 and Lundstrom, Canadian Patent No. 2,022,857. Both the Kenyan and Lundstrom devices use mechanical means to center the cant during curve sawing and thus disparities on the surface of the cant such as scars, knots, branch stubs and the like tend to disturb the machining operation and produce a xe2x80x9cwavexe2x80x9d in the cant. Also, cants subjected to these curve sawing techniques tend to have straight sections on each end of the cant. This results from the need to center the cam on more than one location through the machine. That is, when starting the cut the cant is centered by two or more centering assemblies until the cant engages anvils behind the chipping heads. When the cant has progressed to the point that the centering assemblies in front of the machine are no longer in contact, the cant is pulled through the remainder of the cut in a straight line. It has also been found that full taper curve sawing techniques, because the cut follows a line approximately parallel to the convex or concave surface of the cant, can only produce lumber that mimics these surfaces, and the shape produced may be unacceptably bowed.
Thus in the prior art, so called arc-sawing was developed. See for example U.S. Pat. Nos. 5,148,847 and 5,320,153. Arc sawing was developed to saw irregular swept cants in a radial arc. The technique employs an electronic evaluation and control unit to determine the best semi-circular arc solution to machine the cant, based, in part, on the cant profile information. Arc sawing techniques solve the mechanical centering problems encountered with curve sawing but limit the recovery possible from a cant by constraining the cut solution to a radial form.
Applicant is also aware of U.S. Pat. No. 4,373,563, U.S. Pat. No. 4,572,256, U.S. Pat. No. 4,690,188, U.S. Pat. No. 4,881,584, U.S. Pat. No. 5,320,153, U.S. Pat. No. 5,400,842 and U.S. Pat. No. 5,469,904; all designs that relate to the curve sawing of two-sided cants. Eklund, U.S. Pat. No. 4,548,247, teaches laterally translating chipping heads ahead of the gangsaws. Dutina, U.S. Pat. No. 4,599,929 teaches slewing and skewing of gangsaws for curve sawing. The U.S. Pat. Nos. 4,690,188 and 4,881,584 references teach a vertical arbor with an arching infeed having corresponding tilting saws and, in U.S. Pat. No. 4,881,584, non-active preset chip heads mounted to the sawbox.
Applicant is aware of U.S. Pat. No. 4,144,782 which issued to Lindstrom on Mar. 20, 1979 for a device entitled xe2x80x9cApparatus for Curved Sawing of Timberxe2x80x9d. Lindstrom teaches that when curve sawing a log, the log is positioned so as to feed the front end of the log into the saw with the center of the log exactly at the saw blade. In this manner the tangent of the curve line for the desired cut profile of the log extends, starting at the front end, parallel with the direction of the saw blade producing two blocks which are later dried to straighten and then re-sawn in a straight cutting gang.
It has been found that optimized lumber recovery is best obtained for most if not all cants if a unique modified polynomial cutting solution is determined for every cant. Thus for each cant a xe2x80x9cbestxe2x80x9d curve is determined, which in some instances is merely a straight line parallel to the center line of the cant, and in other instances a complex curve that is only vaguely related to the physical surfaces of the cant.
Thus it is an object of the present invention to improve recovery of lumber from cants and in particular irregular or crooked cants by employing a xe2x80x9cbestxe2x80x9d curve smoothing technique to produce a polynomial curve, which when modified according to machine constraints results in a unique cutting solution for each cant.
To achieve this objective, in a first embodiment, a two sided cant is positioned and accurately driven straight into an active curve sawing gang, which active chip heads directly in front of the saws, to produce the xe2x80x9cbestxe2x80x9d curve which includes smoothing technology. In one embodiment, a machining center in the form of a profiler cuts at least a third and potentially a fourth vertical face from a cant according to an optimized curve so that the newly profiled face(s) on the cant can be accurately guided or driven into a subsequent curve sawing gang. The profiled cant reflects the xe2x80x9cbestxe2x80x9d curve which includes smoothing technology to limit excessive angles caused by scars, knots and branch stubs; while the gang saw products reflect the previously calculated optimized cutting solution.
Due to an increased incidence of jamming of circular gang saw blades with curve sawing in general, it is another object of the present invention to orient the circular saw sawguides near the first contact point of the cant within the gang saw and still allow the sawguides to be rotated back away from the saw blades, thus allowing the saw blades to be removed more easily in the event of a cant becoming jammed than with other known curve sawing circular gang saws of the known type.
In all embodiments of the integrated motion controlled position-based curve sawing of the present invention, the method of position-based integrated motion controlled curve sawing includes the steps of: transporting a cured elongate workpiece, which may be a cant, in a downstream direction on a transfer means, monitoring, by monitoring means, the position of the workpiece on the transfer means, scanning the workpiece through an upstream scanner to measure workpiece profiles in spaced apart array along a surface of the workpiece, communicating, by communication means, the workpiece profiles to a digital processor, which may include an optimizer, a PLC and a motion controller, computing by the digital processor, a high order polynomial smoothing curve fitted to the array of workpiece profiles of the curved workpiece, adjusting the smoothing curve for cutting machine constraints of downstream motion controlled cutting devices to generate an adjusted curve, generating unique position cams unique to the workpiece from the adjusted curve for optimized cutting by the cutting devices along a tool path corresponding to the position cams, sequencing the transfer means and the workpiece with the cutting devices, sequencing the unique position cams corresponding to the workpiece to match the position of the workpiece, feeding the workpiece on the transfer means longitudinally into cutting engagement with the cutting devices, and actively relatively positioning, by selectively actuable positioning means, the workpiece and the cutting devices relative to each other according to a time-based servo loop updated recalculation, based on said workpiece position, of cutting engagement target position as the workpiece is fed longitudinally so as to position the cutting engagement of the cutting devices along the tool path.
Advantageously, the high order polynomial smoothing curve is an nth degree modified polynomial of the form f(x)=anxn+an-1xn-1+ . . . +a1x+a0, having co-efficient an through a0, and where the co-efficients an through a0 are generated by numerical processing to correspond to, and for fitting a smoothing curve along, the corresponding workpiece profiles.
In one aspect of the present invention, the method includes monitoring, by monitoring means cooperating with the digital processor, of loading of the cutting devices and actively adjusting the workpiece feed speed by a variable feed drive, so as to maximize the feed speed. In a further aspect, the method includes compensating for workpiece density in the adjusting of the feed speed or includes monitoring workpiece density, by a density monitor cooperating with the digital processor, and compensating for the density in the adjusting of the feed speed.
Advantageously, the monitoring of the position of the workpiece includes encoding, by an encoder, translational motion of the transfer means and communicating the encoding information to the digital processor. Further advantageously, the monitoring of workpiece position includes communicating trigger signals from an opposed pair of photoeyes, opposed on opposed sides of the transfer means, to the digital processor.
The first mechanical embodiment consists of, first, an indexing transfer which temporarily holds a cant in a stationary position by a row of retractable duckers or pin stops, for regulated release of the cant onto a sequencing transfer. The sequencing transfer feeds the cant through a scanner, where the scanner reads the profile of the cant and sends the data to an optimizer. The scanner may be transverse or lineal.
An optimizing algorithm in the optimizer generates three dimensional models from the cant""s measurements, calculates a complex xe2x80x9cbestxe2x80x9d curve related to the intricate contours of the cant, and selects a breakdown solution including a cut description by position cams that represent the highest value combination of products which can be produced from the cant. Data is then transmitted to a programmable logic controller (PLC) that in turn sends motion control information related to the optimum breakdown solution to various machine centers to control the movement of the cant and the designated gangsaw products.
Immediately following the scanner is a sequencing transfer that also includes a plurality of rows of retractable duckers and/or pin stops that hold the cants temporarily for timed queued release so as to queue the cants for release onto a positioning device. The positioning device may be merely positioning pins or a fence for roughly centering the cant in front of the gangsaw, or may be a positioning table including positioners having retractable pins that center the cant in front of the gangsaw. The positioner pins retract, the positioning table feeds the cant via sharpchains and driven press rolls, straight into the combination active chipper and saw box.
The gangsaw uses a plurality of overhead pressrolls, and underside circulating sharpchain in the infeed area, with fixed split bedrolls in the infeed area and non-split bedrolls in the outfeed area. A plurality of overhead pressrolls hold the cant from the top and bottom by pressing down onto the flat surface of the cant thus pressing the cant between the lower infeed sharpchain (infeed only) and bedrolls and the overhead pressrolls, for feeding the cant straight into the gang saw. The chipping heads and the saws on the saw arbor may be actively skewed and translated, so as to follow the optimized curve sawing solution. In this fashion the cant moves in one direction only, and the chipping heads and the saws are actively motion controlled to cut along the curved path that has been determined by the optimizer. The chip heads move with the saws to create flat vertical sides on the cant so that there is no need to handle and chip slabs, and no need to install a curve forming canter before the gangsaw.
The chipping heads may be retracted or relieved out away from the preferred curved face of the cant so as to keep the cutting forces equal in the event of a bulge or flare in the thickness of the cant or to reduce motor loading. The use of active chipping heads in this manner allows creating a side board in what would be waste material in the prior art between an outermost saw and a chipping head in the instance where the bulge or flare is substantial enough to contain enough material in thickness and length to create an extra side board. The optimizer would prepare the system to accept the extra side board.
In summary, the active gangsaw of a first mechanical embodiment of the present invention comprises, in combination, an opposed pair of selectively translatable chipping heads co-operating with a gangsaw cluster, wherein the opposed pair of selectively translatable chipping heads are mounted to, and selectively translatable in a first direction relative to a selectively articulatable gangsaw carriage, wherein the first direction crosses a linear workpiece feed path wherealong workpieces may be linearly fed through the active gangsaw so as to pass between the opposed pair of selectively translatable chipping heads and through the gangsaw cluster, and wherein the gangsaw cluster is mounted to the gangsaw carriage and is selectively positionable linearly in the first direction and simultaneously rotatable about a generally vertical axis to thereby translate and skew the workpiece carriage relative to the workpiece feed path by selective positioning means acting on the gangsaw carriage.
Advantageously, the gangsaw carriage is selectively positionable linearly in said first direction by means of translation of said gangsaw carriage along linear rails or the like translation means mounted to a base, and is simultaneously rotatable about said generally vertical axis by means of rotation of said gangsaw carriage about a generally vertical shaft extending between said gangsaw carriage and said base.
The second mechanical embodiment consists of, first, an indexing transfer which temporarily holds a cant in a stationary position by a row of retractable duckers or pin stops, for regulated release onto a sequencing transfer. The sequencing transfer feeds the cart through a scanner, where the scanner measures the profile of the cant and sends the data to an optimizer.
An optimizing algorithm in the optimizer generates three dimensional models from the cant""s measurements, calculates a complex xe2x80x9cbestxe2x80x9d curve related to the interior contours of the cant, and selects a breakdown solution including a cut description by position cams that represents the highest value combination of products which can be produced from the cant. Data is then transmitted to a PLC that in turn sends motion control information related to the optimum breakdown solution to various machine centers to control the movement of the cant and the various devices hereinafter more fully described.
Immediately following the scanner is a sequencing transfer that also includes a plurality of rows of retractable duckers and/or pin stops that hold the cants temporarily for timed queued release so as to queue the cants for release onto a positioning device. The positioning device positions the cant in front of the gangsaw, and in some cases positions the cant in front of selected gangsaw zones that have been determined by the optimizer decision processor to provide the optimum breakdown solution.
A skew angle is calculated by the optimizer algorithm so that the positioning device presents the cant tangentially to the saws. If the positioning device is a skew bar, the skew bar pins retract, the rollcase feeds the cant into a pair of press rolls and then further into a chipper drum and an opposing chipper drum counter force roll. The chipper drum begins to chip and to form the optimized profile onto one side of the cant as the cant moves past it, while the opposing chipper drum roll counters the lateral force created by the chipper drum, to help to maintain the cants"" direction of feed. The cant is driven toward the saws and contacts a steering roll mechanism adjacent the chipper drum in the direction of flow. The steering roll comes into contact with the face that has just been created by the chipper drum. The steering roll has an opposing crowder roll that maintains a force against the steering roll while being active so as to move in and out to conform to the rough side of the cant as it moves toward the saws. A guide roll is positioned to allow the cant to move up to the saws in the intended position. The guide roll is adjustable, and also capable of steering when the configuration requires it to steer for different saw configuration and lumber sizes. The guide roll also has an opposing crowder roll that maintains a force against the guide roll while also being active so as to move in and out to conform to the rough side of the cant.
The steering mechanism and the chipper drum are active as the cant proceeds through the saws and are controlled by controllers that use control information from the optimized curve decision, thus controlling the movements of the cant as it proceeds through the apparatus, profiling one face of the cant and cutting the cant into boards as defined in the cutting description.
An alternate embodiment consists of two opposed chipper heads. In this embodiment a cant may be chipped from both sides, with the steering being done from one side or the other, depending on the cant being sawn. Air bags are provided on all steering rolls. The air bags may be locked so as to become solid when being used for steering, and may be unlocked to act as a crowding roll when the opposite side is doing the steering.
Alternatively, a plurality of overhead press rolls, and underside fixed rolls hold the cant from the top and bottom by pressing down onto the flat surface of the cant thus pressing the cant between the lower rolls and the overhead press rolls. The cant is fed straight into the gang saw and the gangsaw translated and skewed so as to follow the optimized curve sawing solution.
In summary, in a second mechanical embodiment of the present invention, a cant, having been scanned by a scanner, is transferred onto a positioning means such as a positioning roll case where the positioning means includes means for selectively skewed pre-positioning of a cant upstream of a selectively and actively positionable cant reducing means such as a chipper head for forming either a curved third face or curved third and fourth faces on the cant. The device further includes an upstream pair of opposed selectively actively positionable cant guides and a downstream pair of opposed selectively actively positionable cant guides, the upstream pair of guides being downstream of the cant reducing means and the downstream pair of guides being upstream of gang saws mounted on a saw arbor. The upstream and downstream pair of guides are aligned, with one guide of each pair of guides generally corresponding with the cant reducing means on a first side of the cant transfer path. The opposed guides in the two pairs of guides are in opposed relation on the opposing side of the cant transfer path and are generally aligned with a cant positioning means along the cant transfer path. The cant positioning means is in opposed relation to the cant reducing means, that is, laterally across the cant transfer path.
In addition, either in combination with the above or independently, the gang saws and saw arbor may be selectively actively positionable both laterally across the cant transfer path and rotationally about an axis of rotation perpendicular to the cant transfer path so as to orient the gang saws to form the curved face on the rough face of the cant and to form a corresponding array of parallel cuts by the gang saws corresponding thereto.
In a further aspect, the selectively actively positionable cant reducing means is an opposed pair of selectively actively positionable cant reducing means such as an opposed pair of chipper heads placed in spaced apart relation on either side laterally across the cant transfer path.
In a further aspect, the pairs of selectively actively positionable cant guides includes actively positionable cant guides on the side of the cant corresponding to the actively positionable cant reducing means and on the opposing side laterally across the cant transfer path, the cant guides on the side of the cant transfer path corresponding to the cant positioning means or, in the embodiment having opposed pairs of selectively actively positionable cant reducing means, the side of the cant transfer path corresponding to the cant reducing means which is selectively deactivated so as to become a passive guide.
The third mechanical embodiment consists of, first, an indexing transfer which temporarily holds a cant in a stationary position by a row of retractable duckers or pin stops, for regulated release onto a sequencing transfer. The sequencing transfer feeds the cant through a scanner, where the scanner reads the profile of the cant and sends the data to an optimizer.
An optimizing algorithm in the optimizer generates three dimensional models from the cant""s measurements, calculates a complex xe2x80x9cbestxe2x80x9d curve related to the intricate contours of the cant, and selects a breakdown solution including skew angles and a cut description by position cams that represents the highest value combination of products which can be produced from the cant. Data is then transmitted to a PLC that in turn sends motion control information related to the optimum breakdown solution to various machine centers to control the movement of the cant and the cutting of both a profiled cant and the designated gangsaw products.
Immediately following the scanner is a sequencing transfer which feeds a profiler positioning table and subsequently a profiler. The sequencing transfer includes a plurality of rows of retractable duckers or pin stops perpendicular to the flow that hold the cant temporarily for timed release so as to queue the cant for delivery onto the profiler positioning table.
The profiler positioning table locates and skews the cant to a calculated angle for proper orientation to the profiler and then feeds the cant linearly into the profiler whereby it removes the vertical side face(s). The newly profiled face or faces, used to steer the cant through the gang saws, follow the optimum curve calculated by the computer algorithm from the scanned image of the individual cant. The removal of superfluous wood from the vertical face(s) is achieved by the interdependent horizontal tandem movement of opposing chipping heads or bandsaws, substantially perpendicular to the direction of flow.
On the outfeed of the profiler an outfeed rollcase has a jump chain that raises the cant off the rolls and then feeds the cant onto a cant turner were the cant is turned over laterally 180 degrees if necessary to the proper orientation for entry into the curve sawing gang. The jump chain includes a plurality of rows of retractable duckers or pin stops that hold the cant temporarily for timed release to the cant turner.
A sequencing transfer, that also includes a plurality of rows of retractable duckers or pin stops, hold the cant temporarily for timed release so as to queue up the cant for release onto a positioning rollcase. The positioning rollcase includes a skew bar with retractable pins that pre-positions the profiled cant on the correct angle and in front of the selected gangsaw combination that has been determined by the optimizer to provide the optimum breakdown solution. The skew angle is calculated by the optimizer algorithm to present the profiled cant tangentially to the saws. The skew bar pins retract, the rollcase feeds the profiled cant into a steering mechanism, and the steering mechanism, using control information from the optimized curve decision, then controls the movement of the cant as it proceeds through the array of saws, cutting the profiled cant into the boards defined in its cutting description.
In summary, the curve sawing device of a third mechanical embodiment of the present invention comprises a cant profiling means for opening at least a third longitudinal face on a cant, wherein the third face is generally perpendicular to first and second opposed generally parallel and planar faces of the cant, according to an optimized profile solution so as to form an optimized profile along the third face, cant transfer means for transferring the cant from the cant profiling means to a cant skewing and pre-positioning means for selectively and actively controllable positioning of the cant for selectively aligned feeding of the cant longitudinally into cant guiding means for selectively actively laterally guiding and longitudinally feeding the cant as the cant is translated between the cant skewing and pre-positioning means and a lateral array of generally vertically aligned spaced apart saws so as to position the third face of the cant for guiding engagement with cant positioning means, within the cant guiding means, for selectively actively applying lateral positioning force to the third face to selectively actively position the cant within the cant guiding means as the cant is fed longitudinally into the lateral array of generally vertically aligned spaced apart saws.
The curve sawing method of the third mechanical embodiment of the present invention comprises the steps of:
a) profiling a cant by a cant profiling means to open at least a third longitudinal face on a cant wherein the third face is generally perpendicular to the first and second opposed generally parallel and planar faces of the cant, the profiling according to an optimized profile solution generated for the cant so as to form an optimized profile along the third face,
b) transferring the cant by cant transfer means from the cant profiling means to a cant skewing and prepositioning means,
c) skewing and prepositioning the cant by the cant skewing and prepositioning means to selectively and actively controllably position the cant for selectively aligned feeding of the cant longitudinally into cant guiding means,
d) guiding the cant by the cant guiding means for selectively actively laterally guiding and longitudinally feeding the cant as the cant is translated between the cant skewing prepositioning means and a lateral array of generally vertically aligned spaced apart saws,
e) positioning the third face of the cant by cant positioning means within the cant guiding means so as to position the third face of the cant for guiding engagement with the cant positioning means, the cant positioning means for selectively actively applying lateral positioning force to the third face to selectively actively position the cant within the cant guiding means as the cant is fed longitudinally into the lateral array of generally vertically aligned spaced apart saws,
f) feeding the cant longitudinally from the cant guiding means into the lateral array of generally vertically aligned spaced apart saws.
In both the curve sawing device and the curve sawing method of the present invention the cant profiling means may open a third and fourth longitudinal face on the cant wherein the third and fourth faces are generally perpendicular to the first and second opposed generally parallel planar faces of the cant and are themselves generally opposed faces, and wherein within the cant guiding means the cant positioning means comprise laterally opposed first and second positioning force means corresponding to the third and fourth faces respectively to, respectively, actively applied lateral positioning force to selectively actively position the cant within the cant guiding means.
In further aspects of the present invention, the first and second laterally opposed positioning force means each comprise a longitudinally spaced apart plurality of positioning force means. The first positioning force means may include, when in guiding engagement with the third face, longitudinal driving means for urging the cant longitudinally within the cant guiding means.